A technology for grinding an object to be ground has been known (see, for instance, Patent Literatures 1 and 2).
Patent Literature 1 discloses a machine for grinding (surface-processing) a semiconductor wafer (object to be ground) (hereinafter, referred to as a wafer).
This machine is configured to support at least one of rotary shafts respectively provided with ring-shaped surface plates to be pressed on both surfaces of the wafer so that the at least one of rotary shafts is tiltable, measure an inclination angle of the at least one of rotary shafts tiltably supported, estimate a shape of the wafer based on the measured inclination angle, compare the estimated result with a target shape, and tilt the at least one of rotary shafts tiltably supported according to the comparison result.
Patent Literature 2 discloses a method for simultaneously grinding both surfaces of the wafer (object to be ground).
In a machine for implementing this method, the wafer is interposed between and machined by two rotary grinding stones fixed to respective facing collinear spindles. During machining of the wafer, the wafer is guided in an axial direction in a substantially non-binding manner by two hydrostatic bearings, guided in a radial direction by a guide ring, and rotated by a driving device. During grinding of the semiconductor wafer, a distance in the radial direction between at least one of the hydrostatic bearings and the corresponding grinding stone is measured by at least two sensors, horizontal and vertical correction positions of the spindle are calculated based on the measured distance, and the positions of the spindle are corrected according to the calculation results.